Bacterial physiology

Spacers go off-site

During the CRISPR–Cas adaptation process, the Cas1–Cas2 complex inserts new spacers between the leader sequence and the first repeat of the CRISPR array. Now, Nivala et al. report that non-canonical off-target integrations can occur in vivo at CRISPR repeat-like sequences within the genome of Escherichia coli. Most of the off-target spacer integrations occured downstream of endogenous promoters within protein-coding regions of non-essential genes and off-target integration products were shown to be expressed. The authors propose that, although probably mostly deleterious, off-target integration could potentially lead to the expression of functional CRISPR RNAs and increase spacer diversity. They also uncovered putative off-target spacer integration events in previously sequenced genomes of Yersinia pestis and Sulfolobus islandicus, and termed the phenomenon of non-canonical spacer integration 'neo-CRISPR genesis'.

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    Nivala, J., Shipman, S. L. & Church, G. M. Spontaneous CRISPR loci generation in vivo by non-canonical spacer integration. Nat. Microbiol. https://doi.org/10.1038/s41564-017-0097-z (2018)

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Du Toit, A. Spacers go off-site. Nat Rev Microbiol 16, 122 (2018). https://doi.org/10.1038/nrmicro.2018.20

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